Every four years Supreme Court watchers try to guess how many Justices the next President will be able to appoint — and what those new appointees would mean for the law. For some reason, during this campaign season the media and the public do not seem to be thinking much about this question — far less, say, than about shirtless photos of a vice-presidential candidate — but they should be. It’s not just a legal parlor game: court appointments over the next four years could rewrite the rules for everything from gun control to abortion rights.

There is no way of knowing how many vacancies there will be during the next presidential term, since Justices are appointed for life. But there is a reasonable chance that there could be one or more. Four of the current Justices are over 74, including Stephen Breyer, who turned 76 last week, and Ruth Bader Ginsburg, who is 79. Justices sometimes step down for personal reasons, as Sandra Day O’Connor and David Souter did in recent years.

Even a single Justice can have a profound impact on the country. We saw just how profound this year, with the Supreme Court’s 5-4 ruling upholding the new national health care law. With the Supreme Court sharply divided along ideological lines — as it has been for years — there are a large number of hot-button issues on which one new Justice could make a major difference.

Take campaign finance, for example. In 2010, the court handed down a controversial ruling in Citizens United v. Federal Election Commission, holding that corporations have a constitutional right to spend unlimited amounts of money on federal elections. The most important issues in the case were decided by a 5-4 vote. This ruling was wildly unpopular — one poll found that 62% of Americans oppose it. But the court shows no signs of backing away from it.

Supporters of campaign-finance restrictions have been talking about trying to undo it by passing a constitutional amendment, but the best chance of reining in corporate influence on elections would be if President Obama is re-elected and one of the conservative Justices left the Court. If that happened, there might well be five votes to overturn the Citizens United ruling.

Guns are another issue on which a single appointment could make a huge difference. In 2008, the Supreme Court struck down the gun-control law of Washington, D.C., and held for the first time that the Second Amendment protects an individual’s right to own guns. The court decided this case, District of Columbia v. Heller, by a 5-4 vote. But if President Obama were to replace one of the conservative justices, the court could overturn Heller — giving government far more leeway to pass gun-control laws.

On the other hand, if Mitt Romney is elected and one of the liberal Justices departed, the court could rewrite constitutional law on issues like gay rights and abortion. In 2003, the Supreme Court ruled that laws criminalizing gay sex are unconstitutional. If Romney, as President, got to replace one of the liberal Justices, there could be five votes to allow states to pass these laws again.

A Romney presidency could also mean the end of Roe v. Wade, the landmark 1973 decision establishing the constitutional right to abortion. Romney recently said that he would “love” it if the court reversed Roe. Predicting votes on the court is hardly a science, but some court watchers believe that the addition of one more conservative Justice could ensure that the ruling is overturned. If that happened, states would be free — as they were before 1973 — to make abortion illegal.

There are many other important issues on which a single Supreme Court change could make all of the difference, from whether bans on gay marriage are constitutional to the use of the death penalty to the future of affirmative action. So it is not hard to see why both President Obama and Romney are avoiding talking about it — neither side is eager to take up a subject that has so many hot-button social issues embedded in it. But considering how high the stakes are, voters should be demanding answers from both sides.